Comparison of systemic cytokine levels in patients with acute respiratory distress syndrome, severe pneumonia, and controls

Background-The inflammatory response has been widely investigated in patien ts with acute respiratory distress syndrome (ARDS) and pneumonia. Studies i nvestigating the diagnostic values of serum cytokine levels have yielded co nflicting results and only little information is available for the differen tial diagnosis between ARDS and pneumonia. Methods-Clinical and physiological data, serum concentrations of tumour nec rosis factor (TNF)-alpha, interleukin (IL)-1 beta and IL-6, sand quantitati ve cultures of lower respiratory tract specimens were obtained from 46 pati ents with ARDS and 20 with severe pneumonia within 24 hours of the onset of the disease and from 10 control subjects with no inflammatory lung disease . Cytokine concentrations were compared between groups and determinants in addition to the diagnosis were tested, Results-Serum TNF-alpha levels were significantly higher in ARDS patients ( 67 (57) pg/ml) than in patients with severe pneumonia (35 (20) pg/ml; p = 0 .031) or controls (17 (8) pg/ml; p = 0.007). For IL-1 beta and IL-6 the obs erved differences were not statistically significant between patients with ARDS (IL-1 beta: 34 (65) pg/ml; IL-6: 712 (1058) pg/ml), those with severe pneumonia (IL-1 beta: 3 (4) pg/ml, p = 0.071; IL-6: 834 (1165) pg/ml, p = 1 .0), and controls (IL-1 beta: 6 (11) pg/ml, p = 0.359; IL-6: 94 (110) pg/ml , p = 0.262). TNF-alpha (standardised coefficient: beta = 0.410, p < 0.001) and IL-1 beta (standardised coefficient beta = 0.311, p = 0.006) were most strongly associated with the degree of lung injury, even when the diagnost ic group was included int the statistical model. Conclusions-Serum TNF-alpha levels were higher in patients with ARDS than i n those with severe pneumonia or in control subjects. Multivariate results suggest that the levels of systemic TNF-alpha and IL-1 beta reflect the sev erity of the lung injury rather than the diagnosis.